The present invention relates to a method for the treatment of inner surfaces of a tubular body made of a plastic with low temperature plasma with an object to improve or modify the properties of the surface.
It has been established that the surface properties of shaped articles made of a synthetic plastic resin can be improved or modified when the surface of the article is treated with or exposed to an atmosphere of low temperature plasma with or without deposition of a polymeric substance formed by the plasma. The surface properties improved or modified by the plasma treatment include, for example, affinity with water, printability, adhesivity, anti-electrostatic property and the like as well as the resistance against bleeding or blooming of the plasticizer and other additives contained in the plastic resin on the surface of the shaped article.
The above described effects obtained by the plasma treatment are considerably or sufficiently remarkable but the applicability of the technique of plasma treatment is limited to the outwardly exposed surfaces of shaped articles such as the outer surfaces of sheets, films, rods, tubes, bottles and other irregular forms. For example, the prior art technique of the plasma treatment can hardly be applied to the inner surfaces of hollow bodies such as tubes. This is because no convenient and reliable method was known hitherto for generating stable low temperature plasma in such a confined space surrounded by the plastic walls.
On the other hand, there is a growing demand for the technique of treating inner surfaces of hollow bodies, e.g. tubes, with low temperature plasma. For instance, the tubes and hoses used in the fields of medical technologies and food industries such as the tubes for transfusion of blood and other therapeutic fluids or hoses for transportation of beverages and edible fats or oils as well as many other tubes or hoses for industrial uses must be absolutely free from migration or bleeding of the plasticizer and other additives toward the inner surface thereof. In addition, many tubular bodies used with a medical purpose as embedded in or in contact with the living tissues of human body such as catheters, artificial vascular tracts, artificial esophagi and the like are desired to have improved adaptability to living body, e.g. antithrombosis and adaptability to tissues.
Therefore, development of a convenient and reliable technique for the continuous treatment of inner surfaces of tubular bodies with low temperature plasma is a very urgent problem in the field of plastics processing.